Cancer Risk, Dietary Behavior

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Is there evidence that one such intervention, alone or in combination, is more effective than another in helping individuals or groups modify their diet to consume more fruits and vegetables and less fat?

What is the evidence for the efficacy of dietary interventions by population subgroup, particularly by ethnicity and gender?

What conclusions (if any) can be reached about the cost-effectiveness of these types of interventions?

Search Strategy: To identify articles publishing the results of behavioral dietary interventions, the reviewers performed literature searches in six databases (MEDLINE®, EMBASE, PsycINFO, CINAHL, AGELINE, and AGRICOLA) using a variety of relevant terms.

Selection Criteria: The initial search strategy excluded studies on the basis of date and language of publication, location of the study, whether a free-living population was involved, size of the sample, and other factors. Only studies reporting intake of fruits and vegetables and dietary fat as primary dietary outcomes were included. The researchers reviewed 907 articles and retained 104 (representing 92 independent studies). These articles presented results for behavioral interventions conducted in a wide range of settings.

Data Collection and Analysis: For each article analyzed, a team of two abstractors compiled information regarding the study methodology and results, and the article's quality. Re-review and reconciliation was performed by the Scientific Director. After completion of data abstraction for the 104 eligible articles, summary Evidence Tables were generated that present key details and findings for all eligible articles. Using this data, three increasingly inclusive types of analyses were performed:

A meta-analysis.

A quantitative analysis of the difference in dietary change between intervention and control groups (a differences-in-deltas approach).

A semiquantitative analysis summarizing the statistical significance of the intervention effect.

The report explores the overall efficacy of behavioral interventions on dietary outcomes and considers the influence of specific intervention and population characteristics.

Main Results: In the studies that were reviewed, dietary interventions were consistently associated with an increase in fruit and vegetable consumption (with greater increases noted for fruit intake). More than three-quarters of the studies reviewed reported statistically significant increases in fruit and vegetable intake (as a combined variable). Using the differences-in-deltas approach, the reviewers determined that the average increase in fruit and vegetable intake reported was 0.6 servings per day, and consistent decreases were noted in the intake of total fat and saturated fat. The mean change in total fat intake was estimated as a 7.3 percent reduction in the percentage of calories from fat.

Interventions appeared to be more successful at positively changing dietary behavior in populations at risk of (or diagnosed with) disease than in healthy populations. Several dietary intervention components appear to be particularly promising in modifying dietary change favorable to cancer risk reduction: social support, goal setting, small groups, food-related activities, and the incorporation of family components.

Conclusions: The dissimilarity across studies in terms of outcome measures, study design, analysis strategy, and intervention technique makes it difficult to draw broad conclusions about the efficacy or effectiveness of behavioral dietary interventions. For example, investigators tended to employ more intensive interventions with high-risk populations, making it difficult to discern whether population or intervention characteristics were primarily responsible for increased change in dietary behavior. However, some intervention components may hold promise for future research efforts.

Very few studies were appropriately designed or reported to allow interpretation of evidence for the efficacy of the interventions by population subgroup, particularly low-income or ethnic subgroups. Despite increased Federal agency funding for dietary intervention research in underserved and minority populations, a serious deficit still exists in good-quality, published research designed to determine the relative efficacy of different intervention approaches in these groups.

Furthermore, few studies followed participants for more than a year, and those that did often showed a falling off in the initial dietary behavior change achieved. Thus, more research is needed to determine the longer-term effectiveness of dietary interventions in both the general population and important subgroups and to evaluate programs specifically designed to prevent relapse over time.

Finally, no studies that met the review criteria provided data on the cost-effectiveness of dietary interventions. Comparing the cost-effectiveness of current and innovative intervention approaches will be critical to assessing their broader applicability.